The present invention relates generally to wireless communication systems, and, more particularly, to a mixed-mode transceiver system for a radiotelephone-pair which permits generation of a communication link with a fixed station of the communication system by the transmission of a code contained in either one of the radiotelephones comprising the radiotelephone-pair.
A communication system which transmits information between two locations includes, at a minimum, a transmitter and a receiver interconnected by a transmission channel. Communication between the transmitter and the receiver is effectuated by transmission of the information, in the form of an information signal, upon the transmission channel.
In one type of communication system, a radio communication system, the transmission channel is comprised of a radio-frequency channel which interconnects the transmitter and the receiver. To transmit an information signal (sometimes referred to as a baseband signal) upon the radio-frequency channel, the information signal must be converted into a form suitable for transmission thereof upon the radio-frequency channel.
Conversion of the information signal (i.e., the baseband signal) into a signal suitable for transmission upon the radio-frequency channel is accomplished by a process referred to as modulation wherein the information signal is impressed upon a radio-frequency electromagnetic wave. The radio-frequency electromagnetic wave is of a frequency of a value within a range of values of frequencies which defines the radio-frequency channel. The radio-frequency electromagnetic wave is commonly referred to as a carrier signal, and the radio-frequency electromagnetic wave, once modulated by the information signal, is referred to as a modulated, information signal.
The information content of the resultant, modulated, information signal occupies a range of frequencies, centered at, or close to, the frequency of the carrier signal. Because the modulated, information signal may be transmitted through free-space upon the radio-frequency channel to transmit thereby the information content of the information signal between the transmitter and the receiver of the communication system, the transmitter and the receiver need not be positioned in close proximity with one another.
Various modulation techniques have been developed to modulate the information signal upon the carrier signal to transmit thereby the information signal upon the radio-frequency transmission channel. Such modulation techniques include, but not by way of limitation: amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM).
The receiver of the communication system which receives the modulated, information signal transmitted upon the transmission channel contains circuitry to detect, or to recreate otherwise, the information signal. Typically, the circuitry of the receiver includes circuitry (sometimes consisting of several stages) to convert downward in frequency the received, modulated, information signal. The process of detecting, or recreating, the information signal is referred to as demodulation, and such circuitry for performing demodulation is referred to as demodulation circuitry.
A plurality of modulated, information signals may be simultaneously transmitted as long as the simultaneously-transmitted, modulated, information signals are comprised of carrier signals of dissimilar frequencies, and the resultant, modulated, information signals do not overlap in frequency.
A receiver includes tuning and other filter circuitry to pass only certain of the signals received by the receiver. Such tuning and other filter circuitry form frequency passbands for passing signals, or component portions of signals, having frequencies within the passbands of such circuitry.
The broad range of frequencies of which the carrier signal may be comprised, and upon which the information signal may be modulated, is referred to as the electromagnetic frequency spectrum. Regulatory bodies have divided the electromagnetic frequency spectrum into frequency bands; the frequency bands may be further divided into frequency channels, such channels may, for example, form the transmission channels, as above-described, of a communication system. Regulation of the transmission of radio-frequency signals in certain of the frequency bands of the electromagnetic frequency spectrum minimize interference between simultaneously-transmitted, modulated, information signals.
Portions of a 100 MHz frequency band extending between 800 MHz and 900 MHz are allocated in the United States for radiotelephone communication. Radiotelephone communication, may, for example, be effectuated by a radiotelephone (or other transceiver) utilized in a cellular, communication system. A radiotelephone is operative both to transmit and to receive radio-frequency, modulated, information signals. Two-way communication is permitted between the radiotelephone and a remotely-located transceiver.
In general, a cellular, communication system is comprised of a fixed communication network which transmits modulated, information signals to, and receives modulated, information signals from, radiotelephones. The fixed, communication network is created by positioning numerous base stations at spaced-apart locations throughout a geographical area. A base station forms a fixed site which contains circuitry to receive modulated, information signals transmitted by one, or many, radiotelephones, and to transmit modulated, information signals to the one, or many, radiotelephones. Because both the fixed site formed of the base station and a radiotelephone permits both transmission and reception of modulated, information signals, two-way communication between a radiotelephone and a base station is permitted. The base stations are connected to a conventional, wireline telephone system through switching centers.
The position at which each of the base stations of the cellular, communication system is located is carefully selected so that at least one base station is within the reception range of a radiotelephone positioned at any location throughout the geographical area. Because of the spaced apart nature of the positioning of the base stations, portions of the geographical area throughout which the base stations are located are associated with individual ones of the base stations. Portions of the geographical area positioned proximate to each of the spaced-apart base stations define "cells" wherein a plurality of cells, each associated with a base station, together form the geographical area encompassed by the cellular, communication system. A radiotelephone positioned within the boundaries of any of the cells of the cellular, communication system may transmit, and receive, modulated, information signals to, and from, at least one base station.
Radiotelephones utilized in such a cellular, communication system are of many varied constructions. One construction of radiotelephone, referred to generically as a mobile radiotelephone, is affixed in position in a vehicle, such as an automobile. Affixation of the mobile radiotelephone in the vehicle is advantageous for the reason that the power required for operation of the mobile radiotelephone may be supplied by the vehicular power supply. Therefore, the mobile radiotelephone may be operated at relatively high power levels to increase the transmission range, and reception range, of modulated, information signals transmitted by the mobile radiotelephone. However, because the mobile radiotelephone is affixed in position within the vehicle, portability of the mobile radiotelephone is minimal in some constructions, and in other constructions, although permitting of removal from the vehicle, the portability of the radiotelephone is limited due to the generally large physical size of the mobile radiotelephone. Further, because the mobile radiotelephone is powered by the vehicular power supply when affixed to the vehicle, subsequent to removal of the mobile radiotelephone from the vehicle, an alternate source of power is required to permit operation of the mobile radiotelephone.
Portable radiotelephones are of constructions to permit convenient carriage by a user. To permit such portability, a portable power supply (e.g., a battery pack) is affixed to the portable radiotelephone to power the portable radiotelephone thereby. Because the portable power supply stores only a finite amount of energy, the time period during which the portable radiotelephone may be powered is limited. Once the stored energy of a portable power supply is depleted beneath a minimum level, the supply must be replaced with another portable power supply to permit continued operation of the portable radiotelephone.
To increase the length of time during which the portable radiotelephone may be powered by a single portable power supply, attempts are made to minimize the power level at which the portable radiotelephone is operated, and generally, the maximum power level at which the portable radiotelephone may be operated is less than the maximum power level at which the mobile radiotelephone may be operated. The maximum transmission and reception range of a portable radiotelephone is, therefore, generally less than the maximum transmission and reception range of a mobile radiotelephone.
It may be discerned that radiotelephones are constructed to optimize certain design parameters. Optimization of certain of the design parameters prevents optimization of other of the design parameters. For instance, a portable radiotelephone design optimizes the physical dimensions thereof to increase thereby the portability of the device. The maximum output power of such a portable radiotelephone cannot be optimized, as the size of the power supply would be too large. Conversely, a mobile radiotelephone may be constructed to maximize operational power output levels as a mobile radiotelephone generally need not optimize size parameters.
In the past, therefore, careful consideration of the intended use of the radiotelephone was required to ensure that the radiotelephone was of a construction which optimized desired ones of the design parameters.
The need of a user alternately to utilize a mobile radiotelephone in which certain ones of the design parameters are optimized, and a portable radiotelephone in which other ones of the design parameters are optimized in some instances requires the user to purchase both a mobile radiotelephone and a portable radiotelephone. In the past, when a user required both a mobile radiotelephone and a portable radiotelephone, payment of an access fee was required to provide each of the radiotelephones with distinct access codes to permit each of the radiotelephones to access the communication network (i.e., the fixed sites comprised of the spaced-apart base stations) of the cellular, communication system. Even when simultaneous use of the two telephones was not anticipated or desired, the user was required to obtain such access codes for each radiotelephone.
Disclosed in U.S. Pat. No. 5,029,233, by Michael P. Metroka, co-inventor of the present invention, is a radio arrangement in which two separate radiotelephones are intercoupled such that an access code, required to form the communication link with the communication network, contained in one of the radiotelephones may be transferred to the other of the radiotelephones to permit the other of the radiotelephones to form a communication link with the communication network. Such an arrangement is advantageous as a user is required to obtain only one access code, and, hence, pay only one access fee, but is still able to utilize both of the radiotelephones.
As an example, a user having both a mobile radiotelephone and a portable radiotelephone may pay an access fee to provide the portable radiotelephone with an access code to permit thereby the portable radiotelephone to form a communication link with the communication network. By intercoupling the portable radiotelephone containing the access code with the mobile radiotelephone, the access code contained in the portable radiotelephone may be transferred to the mobile radiotelephone. The access code transferred to the mobile radiotelephone may be utilized by the mobile radiotelephone to form a communication link with the communication network. One such radiotelephone arrangement is the 9800XL extended system sold by Motorola, Inc. The access code contained in one of the radiotelephones is conventionally contained (but not by of necessity) in the portable radiotelephone as, once the user exits the vehicle in which the mobile radiotelephone is affixed, the portable radiotelephone may be carried by the user and then thereafter be utilized to form a communication link with the communication network to communicate therethrough.
Increased usage of cellular, communication systems has resulted, in many instances, in the full utilization of every available transmission channel of the frequency band allocated for cellular, radiotelephone communication. As a result, various ideas have been proposed to utilize more efficiently the frequency band allocated for radiotelephone communications. More efficient utilization of the frequency band allocated for radiotelephone communication increases the transmission capacity of a cellular, communication system.
One such manner by which the transmission capacity of the cellular, communication system may be increased is to utilize a digital, or other discrete, modulation technique. When an information signal is converted into discrete form, a single transmission channel may be utilized to transmit, sequentially, more than one signal. Because more than one information signal may be transmitted upon a single transmission channel, the transmission capacity of an existing frequency band may be increased by a multiple of two or more.
Another such manner by which the transmission capacity of the cellular, communication system may be increased is to reduce the bandwidth of each transmission channel upon which the modulated, information signal is transmitted. Such a reduction in the bandwidth allocated for each transmission channel, of course, requires the bandwidth of the modulated, information signal to be commensurately reduced. For example, by reducing the bandwidth of each of the transmission channels of the allocated frequency band by a factor of two, the transmission capacity of an existing frequency band may be increased by a multiple of two. Reduction in the bandwidth of the transmission channels by other multiples, of course, results in a similar, corresponding increase in transmission capacity.
Adoption of any of the above-mentioned ideas for increasing transmission capacity of an existing, cellular system would require use of a radiotelephone construction capable of generating modulated, information signals which may be transmitted upon such a system of increased capacity. For instance, utilization of a digital, or other discrete, modulation technique would require a radiotelephone capable of forming a discretely-encoded, modulated, information signal. Similarly, utilization of a reduced-bandwidth, modulation technique would require a radiotelephone capable of forming a modulated, information signal of the reduced bandwidth.
The great majority of existing radiotelephones are of constructions which permit transmission of modulated, information signals upon existing cellular, communication systems. Such existing radiotelephones do not generate modulated, information signals capable of generating the signals, as above-described, required to utilize advantageously proposed, cellular communication systems of increased capacity. Therefore, to obtain benefit of the increased capacity of proposed, cellular, communication systems, purchase of radiotelephones of new design would be required.
To permit continued use of existing radiotelephone constructions, systems proposed to implement any of the above-mentioned ideas permit both use of radiotelephone constructions of existing design as well as radiotelephone constructions of designs permitting advantageous utilization of the systems of increased capacity. Radiotelephone constructions of existing design are still, and would remain, quite functional and operable in such systems of increased capacity. Additionally, in many instances, the transmission channels of the frequency band allocated for cellular, radiotelephone communication are fully utilized during only certain periods of the day (for example, during morning and evening rush hour time periods). Further, only certain, cellular systems, generally those located at, or close to, certain urban centers, have reached such full utilization of the existing frequency band. In short, even with the introduction of such systems of increased capacity, radiotelephone constructions of existing design will still be quite useful.
Therefore, because radiotelephones of existing construction may be utilized even subsequent to implementation of cellular systems of increased capacity, utilization of such radiotelephones of existing design will certainly continue. However, such continued use of radiotelephone constructions of existing design would not permit advantageous utilization of the additional transmission capacity of a cellular, communication system of increased capacity. What is needed, therefore, is a system which permits a radiotelephone construction of existing design to utilize the features of a cellular, communication system of increased capacity at minimal cost.